Contact structures with blades having a wiping motion

ABSTRACT

An apparatus providing improved interconnection elements and tip structures for effecting pressure connections between terminals of electronic components is described. The tip structure of the present invention has a sharpened blade oriented on the upper surface of the tip structure such that the length of the blade is substantially parallel to the direction of horizontal movement of the tip structure as the tip structure deflects across the terminal of an electronic component. In this manner, the sharpened substantially parallel oriented blade slices cleanly through any non-conductive layer(s) on the surface of the terminal and provides a reliable electrical connection between the interconnection element and the terminal of the electrical component.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of electricalinterconnection (contact) elements, and, more particularly, tointerconnection elements and tip structures suitable for effectingpressure connections between electronic components.

2. Description of the Related Art

Generally, interconnections between electronic components can beclassified into the two broad categories of “relatively permanent” and“readily demountable”. An example of a relatively permanent connectionis a solder joint. Once two electronic components are soldered to oneanother, a process of unsoldering must be used to separate thecomponents. A wire bond, such as between a semiconductor die and theinner leads of a semiconductor package (or the inner ends of lead framefingers) is another example of a relatively permanent connection.

One example is a group of rigid of pins of pins electronic componentbeing received by resilient socket elements of another electroniccomponent. The socket elements exert a contact force (pressure) on thepins in an amount sufficient to ensure a reliable electronic connectiontherebetween. Another type of readily demountable connection areinterconnection elements (also referred to herein as springs, springelements, spring contacts or spring contact elements) that arethemselves resilient, springy, or mounted in and/or on a spring medium.An example of such a spring contact element is a needle of a probe cardcomponent. Such spring contact elements are typically intended to effecttemporary pressure connection, such as a semiconductor device undertest.

Tip structures are often mounted (or affixed or coupled) to one end ofan interconnection element. Tip structures provide a desired tip shapeto the interconnection elements and are particularly useful in providinga small area contact with a controlled geometry that creates arepeatable high pressure. Tip structures become increasingly critical asthe interconnection elements themselves become smaller and smaller. Atip structure may also have topological features on its surface toassist in providing an electrical contact between the two electricalcomponents. For example, the purpose of the tip structure is typicallyto break through the nonconductive layer (often corrosion, oxidationproducts, or other types of contaminated films) on the terminals of theelectrical component under test. As a contact force is applied, theinterconnection element applies a pressure to the terminal of theelectronic component under test and causes the tip structure to deflectacross the terminal. This small horizontal movement of the tip structureacross the surface of the corresponding terminal allows the tipstructure to penetrate the nonconductive layer on the terminal, therebyestablishing a good electrical contact between the two electroniccomponents. For example, tip structure 10 mounted to interconnectionelement 12 (shown in FIGS. 1A and 1B) has a blade 14 that scrapes asidethe non-conductive layer in order to achieve an electrical contact.

There are a number of problems associated with achieving theabove-described electrical contact. First, as the terminal contact areasalso get smaller, the horizontal movement of the tip structure 10becomes an issue. Second, as the tip structure 10 is forced to deflectacross the terminal (see FIG. 1B), it may also be forced down and awayfrom the terminal causing the blade 14 of the tip structure 10 to rotateaway from the terminal. The rotation of the blade 14 away from theterminal of the electronic component under test reduces the chances ofthe tip structure achieving a dependable electrical contact with theterminal of the electronic component. Further, as the tip structurescrapes across the non-conductive surface of the terminal in an effortto penetrate the nonconductive surface and establish a good electricalcontact, stray particles and buildup often occur along the blade 14 andupper surface of the tip structure 10. This buildup may contribute tohigh contact resistance between the tip structure and the terminal,which may cause inaccurate voltage levels during device testing due tothe voltage produced across the tip structure. The inaccurate voltagelevels may cause a device to incorrectly fail, resulting in lower testyields when the contact is used in a device testing environment.

Thus, an interconnection element and tip structure that minimize buildupalong the blade of the tip structure and maximize contact pressurebetween the tip structure and the terminal of the electronic componentunder test as the tip structure deflects across the surface of theterminal is desired.

SUMMARY OF THE INVENTION

An apparatus and method providing improved interconnection elements andtip structures for effecting pressure connections between terminals ofelectronic components is described. The tip structure of the presentinvention has a sharpened blade oriented on the upper surface of the tipstructure such that the length of the blade is substantially parallel tothe direction of horizontal movement of the tip structure as the tipstructure deflects across the terminal of an electronic component. Inthis manner, the sharpened substantially parallel oriented blade slicescleanly through any non-conductive layer(s) on the surface of theterminal and provides a reliable electrical connection between theinterconnection element and the terminal of the electrical component.

DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side view of an interconnection element and tip structureknown in the prior art.

FIG. 1B is a side view of an interconnection element and tip structure,known in the prior art, under deflection.

FIG. 2A is a side view of an interconnection element and tip structureof the present invention.

FIG. 2B is a pictorial illustration of one embodiment of a tip structureof the present invention.

FIG. 2C is a side view showing an interconnection element and tipstructure of the present invention under deflection.

FIG. 2D is a side view of an alternative embodiment of the presentinvention showing an interconnection element having a substantiallyparallel oriented blade at one end.

FIG. 3A is a cross-sectional view of an elongate interconnectionelement.

FIG. 3B is a cross-sectional view of an elongate interconnectionelement.

FIG. 3C is a cross-sectional view of an elongate interconnectionelement.

FIG. 4A is a pictorial illustration of a generalized embodiment of theinvention, showing prefabricated contact tip structures and theinterconnection elements to which they will be joined.

FIG. 4B is a cross-sectional side view of the contact tip structures ofFIG. 4A joined by brazing to the interconnection elements of FIG. 4A.

FIG. 4C is a cross-sectional side view of the contact tip structures ofFIG. 4A joined by brazing to the interconnection elements of FIG. 1A,after the sacrificial substrate is removed.

FIGS. 5A-5C are cross-sectional views of steps in a process ofmanufacturing cantilevered tip structures on a sacrificial substrate forinterconnection elements, according to an embodiment of the invention.

FIG. 5D is a pictorial illustration of an embodiment of a cantileveredtip structure formed on a sacrificial substrate, according to aninvention.

FIG. 5E is a pictorial illustration of a second embodiment of acantilevered tip structure formed on a sacrificial substrate, accordingto an invention.

FIG. 5F is a side-view showing the cantilevered tip structure of FIG. 5Emounted to a raised interconnection element on a surface of anelectronic component.

FIG. 5G is a front view of the cantilevered tip structure of FIG. 5Emounted to a raised interconnection element on a surface of anelectronic component.

FIG. 5H is a cross-sectional view of a cantilevered tip structure as maybe mounted to a raised interconnection element.

FIG. 5I is a side cross-sectional view of another embodiment offabricating cantilevered tip structures, according to an alternateembodiment of the present invention.

FIG. 5J is a front cross-sectional view of the embodiment illustrated inFIG. 5I.

FIG. 5K is a side cross-sectional view of the cantilevered tip structureillustrated in FIGS. 5I and 5J and mounted to an electronic component,according to an alternate embodiment of the present invention.

FIG. 6A is a pictorial illustration of a tip structure of the presentinvention having a blade having pyramidal edges.

FIG. 6B is a pictorial illustration of a tip structure of the presentinvention having diamond shaped edges.

FIG. 7A is a top view of a tip structure of the present invention havingtwo blades.

FIG. 7B is a cross-sectional view of a tip structure of the presentinvention having two blades joined by a bridge.

FIG. 7C is a cross-sectional view of a tip structure of the presentinvention having two blades in a juxtaposed position.

FIG. 8A is a pictorial illustration of a tip structure of the presentinvention having a blade with a primary blade and a trailing blade.

FIG. 8B is a cross-sectional view of the tip structure of FIG. 8A.

FIG. 9A is a cross-sectional view of a tip structure and substantiallyparallel oriented blade of the present invention affixed to Cobra styleprobes.

FIG. 9B is a cross-sectional view of Cobra style probes having asubstantially parallel oriented blade at one end.

FIG. 10 is a pictorial illustration of a tip structure of the presentinvention having a stand-off blade.

DETAILED DESCRIPTION OF THE INVENTION

An apparatus and method that provides improved interconnection elementsand tip structures suitable for effecting pressure connections betweenterminals of electronic components is described. In the followingdescription, numerous specific details are set forth such as materialtypes, dimensions, processing steps, etc., in order to provide a morethorough understanding of the present invention. However, it will beobvious to one of skill in the art that the invention may be practicedwithout these specific details. In other instances, well-known elementsand processing techniques have not been shown in particular detail inorder to avoid unnecessarily obscuring the present invention. Further,although the present invention is discussed with respect to use as aneedle of a probe card component that provides an electrical connectionbetween the probe card and a terminal of an electrical component undertest, the present invention is not limited to use in a probe card andmay be used to provide electrical connections between other electricalcomponents under other circumstances.

Overview of Present Invention

As previously discussed, there are a number of problems associated withusing the interconnection elements and tip structures currently known inthe art to achieve a good electrical contact between two electroniccomponents. The present invention addresses these problems by providingan interconnection element having a tip structure with a sharpened bladeoriented on the upper surface of the tip structure such that the lengthof the blade runs substantially parallel (within approximately ±15° ofparallel) to the direction of horizontal movement of the tip structureas the tip structure deflects across the terminal of the electroniccomponent under test. Through use of the present invention, a reliableelectrical contact is established between the electronic components.Once the tip structure contacts the terminal of the electroniccomponent, the interconnection element forces the tip structure todeflect across the surface of the terminal such that the tip structureblade slices through (penetrates) the non-conductive layer(s) on thesurface of the terminal. The electronic component may be an integratedcircuit, an interconnect board, a semiconductor wafer, or a printedcircuit board.

FIG. 2A is a side view of the present invention, showing a springcontact element 24 coupled to a substrate 26 at one end and having a tipstructure 20 coupled thereto at an opposite end. FIG. 2B is a pictorialillustration of the tip structure 20 of the present invention, having ablade 22 on the upper surface of the tip structure 20. In thisembodiment of the present invention, the blade 22 comprises a contactelement whose faces when extended form a line in space. When the tipstructure 20 is placed in contact with a terminal of an electroniccomponent (not shown) and a force is applied, the tip structure 20 willdeflect across the surface of the terminal. As the tip structure 20deflects across the terminal, the blade 22 of the tip structure 20 willpenetrate the non-conductive layer on the surface of the terminal. FIG.2C is a side view of the present invention. The dashed lines of FIG. 2Cshow the interconnection element 24 and tip structure 22 after thedeflection across the terminal. ΔX represents the amount of lateral (orhorizontal) deflection of the tip structure 20.

The blade 22 is oriented on the upper surface of the tip structure 20such that the length (L) of the blade is substantially parallel to thedirection of horizontal movement (ΔX) of the tip structure 20 as the tipstructure 20 deflects across the surface terminal (see FIG. 2C). Theorientation of the blade 22 substantially parallel to the direction ofhorizontal motion of the tip structure, allows the blade 22 to slice (orcut) through any non-conductive layer(s) on the surface of the terminal.

FIG. 2D illustrates an alternative embodiment of the present invention,wherein the blade 26 is formed at the end of the spring contact element28 itself, rather than being on a separate tip structure. In thismanner, a substantially parallel oriented blade 26 may be formed withouta transferred tip structure (such as tip structure 20 in FIG. 2A). Theblade 26 may be formed at the end of spring contact 28 by severalmethods including but not limited to a plating or machining process(such as the use of a stamp, swage, electropolish, or electrostaticdischarge).

The orientation of the blade 22 on the upper surface of the tipstructure 20 (or the blade 26 formed at the end of spring element 28)substantially parallel to the direction of the horizontal motioncomponent of the tip structure 20 (hereinafter generally referred to asa parallel orientation) provides numerous advantages over prior art tipstructures. First, the parallel orientation of the sharpened edge alongthe length (L) of the blade 22 allows the blade 22 to cut cleanlythrough the non-conductive layer on the terminal and establish a goodelectrical connection with the terminal of the electric component beingtested. In contrast, the substantially perpendicular orientation of theblades of prior art tip structures (i.e. when the length of the blade isoriented on the upper surface of the tip structure substantiallyperpendicular to the direction of the horizontal motion component of thetip structure as the tip structure deflects across the surface of theterminal under test; for example, see blade 14 of FIGS. 1A and 1B)provides a scraping motion across the non-conductive layer. The priorart blade scrapes across the terminal surface much as a bulldozerscrapes aside a layer of dirt. The scraping motion of perpendicularoriented blades may damage the surface of the terminal, often causessignificant wear and tear on the blades resulting in a short life spanof the blades, and often results in a buildup of stray particles and thenon-conductive layers along the blade. In contrast, the paralleloriented blade 22 of the present invention circumvents each of theabove-described problems by following the direction of horizontal motioncomponent of the tip structure and cleanly slicing through thenon-conductive layer on the terminal. Further, there is minimal, if any,buildup along the surface of the blade 22 which results in a lowercontact resistance between the tip structure and the terminal andproduces more accurate voltage levels during testing.

The parallel orientation of the blade 22 also provides a more reliableelectrical connection with the terminal of the electronic componentunder test. As electronic component terminals become smaller, anymovement by the blade becomes significant as the possibility increasesthat any movement will move the blade outside of the terminal such thatthe blade will be unable to establish an electrical contact with theterminal. As shown in FIGS. 1B and 2C, the deflection of the tipstructure (10, 20) across the terminal may depend on both theinterconnection element's material and shape. In one embodiment, the tipstructure deflects along a substantially rotational path having both alateral (or horizontal) and a vertical component to the motion resultingin both a lateral deflection and a vertical deflection as the tipstructure (10, 20) is pushed down and away from the terminal. It ispossible that the perpendicularly oriented blade 14 will be pushedoutside of the terminal contact area as a result of the rotationalmovement of the tip structure 10. In contrast, as the tip structure 20deflects across the terminal, even if part of the blade 22 is movedoutside of the terminal contact area, the remaining length of the blade22 (the trailing end) continues to be within the terminal contact area.Likewise, even as the front end of blade 22 is forced to rotate down andaway from the terminal contact area, the trailing end of the blade 22will remain in contact with the terminal surface. In this manner, theparallel oriented blade 22 of the present invention provides a morereliable electrical connection (or interface) with the terminal of theelectrical component under test.

Components of the Present Invention

The interconnection element and tip structure of the present inventionmay be manufactured by a variety of methods and from a variety ofmaterials. The following methods of manufacturing and types of materialsdiscussed are illustrative examples only and are not intended to limitthe invention in any manner. Other methods and materials known in theart may also be followed and/or used.

Interconnection Element

Existing interconnection elements such as elongate and/or resilientinterconnection elements may be used for the interconnection element ofthe present invention (element 24 of FIG. 2A). When using resilientinterconnection elements, a composite interconnection element is onepreferred form of contact structure (spring or spring-like element).FIGS. 3A-3C illustrate various shapes commonly used for compositeinterconnection elements. The tip structures of the present inventionmay be used on any spring-like elements including those discussed hereinbelow and those shown in U.S. Pat. No. 5,476,211, issued on Dec. 19,1995, assigned to the assignee of the present invention, and which isincorporated herein by reference.

In FIG. 3A, an electrical interconnection element 310 includes a core312 of a “soft” material (e.g., a material having a yield strength ofless than 40,000 psi), and a shell (overcoat) 314 of a “hard” material(e.g., a material having a yield strength of greater than 80,000 psi).The core 312 is an elongate element shaped (configured) as asubstantially straight cantilever beam, and may be a wire having adiameter of 0.0005-0.0030 inches. The shell 314 is applied over thealready-shaped core 312 by any suitable process, such as by a suitableplating process (e.g., by electrochemical plating). It is generallypreferred that the thickness of the shell (whether a single layer or amulti-layer overcoat) be thicker than the diameter of the wire beingovercoated. By virtue of its “hardness”, and by controlling itsthickness (0.00025-0.02000 in.), the shell 314 imparts a desiredresiliency to the overall interconnection element 310. In this manner, aresilient interconnection between electronic components (not shown) canbe effected between the two ends 310 a and 310 b of the interconnectionelement 310.

FIG. 3A illustrates what is perhaps the simplest of spring shapes for aninterconnection element of the present invention, namely, a straightcantilever beam oriented at an angle to a force as indicated by thearrow labeled “F” applied at its tip 310 b. When such a contact force(pressure) is applied by a terminal of an electronic component to whichthe interconnection element is making a pressure contact, the downward(as viewed) deflection of the tip will result in the tip moving acrossthe terminal, in a “wiping” motion. Such a wiping contact ensures areliable contact being made between the interconnection element and thecontacted terminal of the electronic component. The deflection(resiliency) of the interconnection element in general is determined inpart by the overall shape of the interconnection element, in part by thedominant (greater) yield strength of the overcoating material (versusthat of the core), and in part by the thickness of the overcoatingmaterial.

In FIG. 3B, an electrical interconnection element 320 similarly includesa soft core 322 (compare 312) and a hard shell 324 (compare 314). Inthis example, the core 322 is shaped to have two bends, and thus may beconsidered to be S-shaped. As in the example of FIG. 3A, a resilientinterconnection between electronic components (not shown) can beeffected between the two ends 320 a and 320 b of the interconnectionelement 320. In contacting a terminal of an electronic component, theinterconnection element 320 would be subjected to a contact force(pressure), as indicated by the arrow labeled “F”.

In FIG. 3C, an electrical interconnection element 330 similarly includesa soft core 332 (compare 312) and a hard shell 334 (compare 314). Inthis example, the core 332 is shaped to have one bend, and may beconsidered to be U-shaped. As in the example of FIG. 3A, a resilientinterconnection between electronic components (not shown) can beeffected between the two ends 330 a and 330 b of the interconnectionelement 330. In contacting a terminal of an electronic component, theinterconnection element 330 could be subjected to a contact force(pressure), as indicated by the arrow labeled “F”. Alternatively, theinterconnection element 330 could be employed to make contact at otherthan its end 330 b, as indicated by the arrow labeled “F”.

It should be understood that the soft core can readily be formed intoany springable shape—in other words, a shape that will cause a resultinginterconnection element to deflect resiliently in response to a forceapplied at its tip. For example, the core could be formed into aconventional coil shape. However, a coil shape would not be preferred,due to the overall length of the interconnection element and inductance(and the like) associated therewith and the adverse effect of same oncircuitry operating at high frequencies (speeds). Likewise, the coreelement need not have a round cross-section, but may rather be a flattab (“ribbon”) having a generally rectangular cross-section andextending from a sheet. Other non-circular cross-sections, such asC-shaped, I-shaped, L-shaped and T-shaped cross-sections, may also beused for the interconnection element.

The material of the shell, or at least one layer of a multi-layer shell(described hereinbelow) has a significantly higher yield strength thanthe material of the core. Therefore, the shell overshadows the core inestablishing the mechanical characteristics (e.g., resiliency) of theresulting interconnection structure. Ratios of shell:core yieldstrengths are preferably at least 2:1, and may be as high as 10:1. It isalso evident that the shell, or at least an outer layer of a multi-layershell should be electrically conductive, notably in cases where theshell covers the end of the core.

Suitable materials for the core (312, 322, 332) include, but are notlimited to: gold, aluminum, copper, and their alloys. These materialsare typically alloyed with small amounts of other metals to obtaindesired physical properties, such as with beryllium, cadmium, silicon,magnesium, and the like. It is also possible to use silver, palladium,platinum; metals or alloys such as metals of the platinum group ofelements. Solder constituted from lead, tin, indium, bismuth, cadmium,antimony, and their alloys can be used. Generally, a wire of anymaterial (e.g., gold) that is amenable to bonding (using temperature,pressure, and/or ultrasonic energy to effect the bonding) would besuitable for practicing the invention. It is within the scope of thisinvention that any material amenable to overcoating (e.g., plating),including non-metallic material, can be used for the core.

Suitable materials for the shell (314, 324, 334) include, but are notlimited to: nickel, and its alloys; copper, cobalt, iron, and theiralloys; gold (especially hard gold) and silver, both of which exhibitexcellent current-carrying capabilities and good contact resistivitycharacteristics; elements of the platinum group; noble metals;semi-noble metals and their alloys, particularly elements of theplatinum group and their alloys; tungsten and molybdenum. In cases wherea solder-like finish is desired, tin, lead, bismuth, indium and theiralloys can also be used. The technique selected for applying thesecoating materials over the various core materials set forth above will,of course, vary from application-to-application. Electroplating andelectroless plating are generally preferred techniques.

Another type of electrical interconnection element that may be used withthe present invention is a resilient interconnection element that isformed lithographically. An oriented blade of the invention may beformed on a contact end of a lithographically formed resilientinterconnection element. In one example of the invention, an orientedblade may be formed on a sacrificial substrate and then transferred to acontact end of a lithographically formed resilient interconnectionelement.

The interconnection elements of the present invention (element 24 ofFIGS. 2A-2D) can generally be fabricated upon, or mounted to, anysuitable surface of any suitable substrate, including sacrificialsubstrates, then either removed therefrom or mounted to terminals ofelectronic components.

Coupling Interconnection Elements to Tip Structures

FIG. 4A illustrates a generalized embodiment 400 of the inventionwherein a plurality (four of many shown) of contact tip structures 402have been pre-fabricated upon a support (sacrificial) substrate 404, ina manner described hereinbelow. A corresponding plurality (four of manyshown) of interconnection elements 406 are shown in preparation forhaving their free ends 406a joined to the contact tip structures 402 (orvise-versa). The free ends 406 a of the elongate interconnectionelements 406 are distant (distal) from opposite ends (not shown) of theelongate interconnection elements 406 which typically would extend froma surface of an electronic component (not shown) such as a semiconductordevice, a multilayer substrate, a semiconductor package, etc.

FIG. 4B illustrates, in side view, a next step of joining the contacttip structures 402 to the elongate interconnection elements 406 bybrazing. A resulting braze fillet 408 is illustrated. The contact tipstructures 402 are still resident on the sacrificial substrate 404 intheir prescribed spatial relationship with one another. FIG. 4B is alsoillustrative of the contact tip structures 402 being joined to theelongate interconnection elements with conductive adhesive (e.g.,silver-filled epoxy) or the like. An alternate method of joining thecontact tip structures 402 to the elongate interconnection elements 406is by overcoating at least the junction of the contact tip structures402 and adjacent end portions of the elongate interconnection elements406 with a metallic material such as nickel, by plating.

FIG. 4C illustrates, in a side view, a subsequent step, wherein, afterjoining the contact tip structures 402 to the elongate interconnectionelements 406, the support (sacrificial) substrate 404 is removed. Theresulting “tipped” interconnection element 406 (as used herein, a“tipped” interconnection element is an interconnection element which hashad a separate contact tip structure joined thereto) is shown as havinghad a contact tip structure 402 brazed (408) thereto, in the mannerdescribed with respect to FIG. 4B.

In the embodiments described herein of forming free-standinginterconnection elements (either by themselves, or upon prefabricatedtip structures) on sacrificial substrates, the discussion has generallybeen directed to bonding an end of the interconnection element (or, inthe case of a composite interconnection element, bonding an elongatecore) to a sacrificial substrate. It is within the scope of thisinvention that instrumentalities (techniques) other than bonding can beemployed.

Tip Structures

FIGS. 5A-5H illustrate a technique 500 for fabricating tip structureshaving a parallel oriented blade and mounting same to interconnectionelements which may serve as terminals of electronic components, andFIGS. 5I-5K illustrate an alternate technique 550 employing such tipstructures. These techniques are particularly well suited to ultimatelymounting freestanding interconnection elements to electronic componentssuch as semiconductor devices, space transformer substrates of probecard assemblies, and the like.

FIG. 5A illustrates a sacrificial substrate 502, such as a wafer ofmonocrystalline silicon, into a surface of which a plurality (one ofmany shown) of trenches 504 are etched. A patterned masking layer, suchas a photoresist (not shown), is first patterned on the substrate 50 todefine the length and width of the trench 504. Next, the trench 504 isformed in the substrate 504. In the preferred embodiment, a potassiumhydroxide (KOH) selective etch is performed between the 111 and 001crystal orientation.

Note that methods other than a KOH selective etch may be used to formthe trench 504 used to form the blades of the present invention. Forexample, the trenches may also be formed with a reactive ion etch (RIE).Further, non-lithographic methods may also be employed, including butnot limited to polishing (both electro-polishing and mechanicalpolishing) stamping, or abrading the tip structures. Combinations ofstraight walled and trenched structures may also be produced bycombining different etching techniques. Such combinations may bedesirable to create stand-off structures such as the one illustrated inFIG. 10. As with the tip structures discussed herein above, tipstructure 980 is comprised of a tip base 982 and tip blade 984. Tipstructure 980, however, also includes a straight-walled section 986 thatprovides the stand-off distance (D) for the tip structure 980.

The preferred embodiment comprises a tip structure with a blade on theupper surface, wherein the blade has a sharpened edge along the lengthof the blade and a triangular cross-section. However, the trenches 504are merely illustrative of any surface texture ‘template’ for the tipstructures which will be fabricated on the sacrificial substrate 502.The layout (spacing and arrangement) of the trenches 504 can be derivedfrom (replicate) the bond pad layout of a semiconductor die (not shown)which is ultimately (in use) intended to be contacted (e.g., probed) byfree-standing interconnection elements to which the tip structures 504are ultimately attached. For example, the trenches 504 can be arrangedin a row, single file, down the center of the sacrificial substrate.Many memory chips, for example, are fabricated with a central row ofbond pads.

FIG. 5B illustrates that a hard “field” layer 506 has been depositedupon the surface of the sacrificial substrate 502, including into thetrenches 504. The field layer 506 will serve as a release layer. Onepossible release layer is comprised of aluminum having an approximatethickness of 5000 Å. Another layer 508 can optionally be deposited overthe field layer 506, if the field layer is of a material which is notamenable to plating. Typically, layer 508 is comprised of copper havingan approximate thickness of 5000 Å. (If the layer 506 is difficult toremove, it may be applied by selective deposition (e.g., patterningthrough a mask), to avoid such removal.) After the contact structuresare fabricated within the trench (see below), the sacrificial substrate502 may be removed by any suitable process, such as by selectivechemical etching.

Note also, however, that in addition to a chemical etchant, appropriatemetallurgy can be used in conjunction with heat to release thesacrificial substrate 502. For example, in one embodiment of the presentinvention, layer 506 comprises a non-wettable material such as tungsten(or titanium tungsten) deposited on the substrate 502 by means such assputtering. Next, the thin layer 508 is deposited comprising anon-wetting material such as plateable lead (or indium) onto thetungsten layer 506. Then, after the contact tip structures arefabricated within the trench (see below), a reflow technique (usingheat) may be used to mount the contact tip structures ontointerconnection elements. During reflow, the lead (material 508) willmelt and ball up, since tungsten (material 506) is not wettable withrespect to lead. This causes the contact tip structures to be releasedfrom the sacrificial substrate 502. Optionally, a second layer (notshown) of non-wettable material (e.g., tungsten) can be applied overlayer 508, and will become part of the resulting contact tip structureunless removed (,e.g., by etching). Further, another layer of materialwhich will ball up when heated (e.g., lead, indium) can be applied overthe second layer of non-wettable material (e.g., tungsten). Any residuallead on the surface of the resulting contact tip structure is readilyremoved, or may be left in place. Alternatively, a layer of a “barrier”material can be deposited between the second layer of material whichwill ball up and the first layer of the fabricated contact tipstructure. The “barrier” material may be tungsten, silicon nitride,molybdenum, or the like.

Once layers 506 and 508 are deposited, a masking material 510(illustrated in FIG. 5C), such as photoresist, is applied to define aplurality of openings for the fabrication of tip structures. Theopenings in the masking layer 510 define a region around the trenches504. First, a contact metal 512 is deposited, typically having a minimumthickness of approximately 0.5 mil. This contact metal may be depositedby sputtering, CVD, PVD, or plating. In one embodiment of the presentinvention, the contact metal 512 is comprised of Palladium-Cobalt. Othermaterials may also be used for contact metal 512, including but notlimited to, palladium, rhodium, tungsten-silicide, tungsten, or diamondNext, layer 514 comprised of a spring alloy material (such as nickel andits alloys) is optionally deposited (such as by plating) to increase thebulk of the tip structure. Layer 514 typically has an approximatethickness of 0-2 mils. Over layer 514, a layer 516 is depositedcomprising a material amenable to brazing or soldering, in the eventthat the spring alloy is not easy to bond, solder or braze to. Thespring alloy layer 514 is deposited by any suitable means such asplating, sputtering, or CVD. Finally, a Au-Braze joining layer 516 isdeposited. The Au-Braze layer is specific to an AuSn braze attach.

Next, as illustrated by FIGS. 5D and 5E, the masking material 510 isstripped (removed), along with that portion of the layers (506 and 508)which underlies, the masking material 510, resulting in a plurality (oneof many shown) of tip structures (520 and 520 a) having been fabricatedupon the sacrificial substrate 502. FIG. 5D shows a first embodiment ofa tip structure 520 of the present invention having a blade 522 thatextends the entire length of the foot of the tip structure 520. FIG. 5Eshows a second embodiment of a tip structure 520 a of the presentinvention having a blade 522 a that extends along a potion of the footof tip structure 520 a. Tip structure 520 a also has a back portion 521wherein the blade 522 a does not extend through the foot of the tipstructure 520 a. The two alternate embodiments of tip structures 520 and520 a serve the same function in providing an electrical contact withthe terminal of an electronic component under test, but providedifferent surfaces for coupling the tip structure 520 and 520 a to aninterconnection element.

FIG. 5F and 5G illustrate the mounting of the tip structures 520 a shownin FIG. 5E to raised interconnection elements 530 extending (e.g.,free-standing) from corresponding terminals (one of many shown) 532 ofan electronic component 534. FIG. 5F shows a side view of mounted tipstructures 520 a and FIG. 5G shows a front view of mounted cantilevertip structures 520. The interconnection element is coupled to the footof the tip structure 520 a along the back portion 521 of the tipstructure 520 a where the blade 522 a does not extend and the surface ofthe foot of the tip structure 520 a is flat. The pre-fabricated tipstructures 520 a is mounted to the tips (top, as shown) of theinterconnection elements 530, in any suitable manner such as brazing orsoldering.

FIG. 5H illustrates the tip structure 520 as shown in FIG. 5D prior tobeing mounted to raised interconnection elements 530 extending (e.g.,free-standing) from corresponding terminals (one of many shown) 532 ofan electronic component 534 (interconnection elements 530, terminals 532and electronic component 534 are not shown in FIG. 5H). In thisembodiment of the present invention, the solder paste or brazingmaterial used to mount the tip structure 520 to the interconnectionelement 530 is positioned within the divot 523. The end result is amounted tip structure similar to that illustrated in FIGS. 5F and 5G,with the interconnection element affixed to the divot 523 rather than aflat back section (see 521 of FIG. 5F). Using the divot formed whenfabricating the blade 522 aids in positioning the solder paste orbrazing material and provides a more reliable method of forming themechanical connection between the interconnection element 530 and thefoot of the tip structure 520.

The raised interconnection elements 530 can be any free-standinginterconnection elements including, but not limited to, compositeinterconnection elements, and specifically including contact bumps ofprobe membranes (in which case the electronic component 534 would be aprobe membrane) and tungsten needles of conventional probe cards. Theinterconnection element may be formed lithographically or through abonding and plating operation as in U.S. Pat. No. 5,476,211. The raisedinterconnection elements, although typically resilient and providing aspring-like motion, may also be rigid posts. Note that the shape of theresilient element to which the tip structures are attached will affectthe wipe characteristic (i.e., the horizontal movement of the tipstructure across the surface of the terminal contact of the device undertest) in probing. External forces, such as machine-controlled movement,may also affect the wipe characteristic. Thus, the interconnectionelements may be designed to optimize a desired contact behavior.

FIGS. 5I-K illustrate another technique 550 of employing tip structures,wherein the tip structures are provided with their own raised contacts(interconnection elements) prior to being mounted to terminals of anelectronic component. This technique commences with the same steps offorming trenches 504 in a surface of a sacrificial substrate 502,applying a field layer 506, applying an optional brazing layer 508, andapplying a masking material 510 with openings defining the locations andshapes of the resulting tip structures. Compare FIGS. 5A-5C above.

In a next step, as illustrated by FIGS. 5I-J (FIG. 5I is a side view andFIG. 5J is a front view), a freestanding interconnection element 552 ismounted to the back end portion of the tip structure 530. Then, with useof a masking layer 510, a layer of hard (springy) material 554 isdeposited over the tip structure (and, optionally, another layer such as516 which is brazeable, see above). The masking layer 510 is stripped,and the tip structure 570 can be mounted to terminals 582 of anelectronic component 584, by soldering or brazing the tips of thefree-standing interconnection elements 552 to terminals 582, asindicated by the solder fillet 586. Note that in the alternate mountingtechnique shown in FIGS. 5I-K, the coupling step (typically soldering orbrazing) occurs when coupling the interconnection element to anelectronic component, wherein with the first mounting techniquedescribed in FIGS. 5A-H, the coupling step joins the tip structure tothe interconnection element. In other words, when contrasting the twomounting techniques, the coupling step of soldering or brazing isperformed on opposite ends of the interconnection element.

In these examples, the interconnection elements 520 and 570 areillustrated as being composite interconnection elements having springshapes, but it should clearly be understood that the invention isexpressly not limited thereto. In either case (500, 550) the result isthat an electronic component (534, 584) is provided with a plurality offree-standing interconnection elements (530, 552) extending fromterminals thereof, the tips (free ends) of the free-standinginterconnection elements 520 being provided with tip structures having asurface texture which is imparted (defined) during the process offabricating the tip structures on the sacrificial substrate 502.

It is evident from the preceding descriptions that the interconnectionelements alone (530, 552 (i.e., 552 overcoated by 554)) need not beresilient. Resilience may the provided by the ability of the cantilevertip structures (520, 570) to deflect in response to making a pressureconnection with another electronic component (not shown) because the tipstructures 504 are disposed along a cantilever beam. Preferably, thefreestanding interconnection elements 520 are much stiffer than thecantilever beams, so that the contact force resulting from a pressureconnection can be well defined and controlled.

In any cantilever beam arrangement, it is preferred that one end of thecantilever be “fixed” and the other end “movable”. The cantilever beammay serve as a foot for a tip structure or a foot of a prefabricated tipstructure may be mounted onto a separately fabricated beam. In thismanner, bending moments are readily calculated. Hence, it is evidentthat the elongate interconnection elements (530, 552) are preferably asrigid as possible. (In the case where the interconnection elements (530)are contact bumps on a membrane probe, resiliency is provided by themembrane (534), itself.) However, it is not entirely inapposite that theelongate interconnection elements are implemented as compositeinterconnection elements, such as the composite interconnection elementsdiscussed above, which will contribute to the overall deflection of thetip structures in response to pressure connections being made to (by)the tip structures.

Alterative Embodiments Utilizing the Present Invention

The cross-section of the tip section blade as discussed above istriangular. However, other cross-sections may also be used. For example,a truncated pyramid could easily be fabricated in a similar manner tothat described above. Note also, that a tip structure initiallyfabricated to have a sharp edge blade along the length of the tipstructure will often become flat-topped as it wears with use. This“flat-top” results in a cross-section very similar to a truncatedpyramid. A tip structure having a truncated pyramid cross-section stillmaintains the benefits of a parallel oriented blade outlined above.

Different embodiments of the parallel oriented blade of the presentinvention may have different front and back edges. For example, in someinstances, the blades may have rectilinear edges (i.e. edges that areperpendicular to the tip structure) such as the blade 522 beingfabricated in FIG. 5D. FIG. 6A shows an alternate blade 600 withpyramidal front and back edges 602. On blade 600, the front and backedges 602 are at an angle larger than 90° from the foot of the tipstructure 604. A second alternate blade 610 having a diamond shape isillustrated in FIG. 6B. Blade 610 is formed by performing a KOH etch at45° relative to the primary axis of the lattice and then defining thephoto resist etch widow as having 6 sides (or as having a hexagonalshape). This results in a tip structure 614 having a diamond shape blade610 on its top surface.

There are many other alternative embodiments that benefit from thenumerous advantages provided by the parallel oriented blade of thepresent invention. For example, more than one blade 700 may befabricated on a tip structure, as shown in a top view of tip structure702 in FIG. 7A. This embodiment would be particularly useful for probingcontrolled collapse chip connection (C4) solder balls or other sphericalstructures.

Another variation of the embodiment of the present invention having twoor more blades fabricated on a single foot is shown in FIG. 7B. FIG. 7Bis a front view of a tip structure 714 showing two blades 710 joined bya bridge 712, and having an included stand-off 716. Additionally, withmultiple blades formed on a tip structure, the pre-determined pitchbetween blades would be particularly useful with spherical probinghaving a fine pitch.

FIG. 7C is a side view of a third embodiment of the present inventionhaving two or more blades fabricated on a single foot. On tip structure724, two blades 720 are placed in a juxtaposed position and share acommon trench 722 having a stand-off height of H. The juxtaposed blades720 are particularly useful in situations for fine pitch applicationswith contact surfaces in close proximity. Another embodiment utilizingthe present invention is a multi-height blade such as blade 800 shown inFIG. 8A and 8B. Blade 800 has a primary blade 802 toward the front edgeof the tip structure 806, and a trailing blade 804 toward the back ofthe tip structure 806. The blade 800 may be formed using a maskingprocess wherein the mask surrounding the shorter, trailing blade 804provides a smaller hole such that the trench etch by the KOH etch isshallow, and the mask surrounding the taller, front blade provides alarger hole such that the trench etch by the KOH etch is deeper and theblade 806 will be taller.

The present invention may also be used with the conventional Cobra styleprobes, a partial view of which is shown in FIG. 9A. Cobra style probesutilize pre-bended contact wires 906 positioned vertically andmaintained by two guide plates 908 and 910. The perforated guide plates908 and 910 hold and direct the wires 906. The Cobra style probes sufferfrom the restriction that the contact geometry is determined by the useof round wire, and that the contact metallurgy is that of the springitself. Use of transferred tip structures of the present invention yielda controlled geometry, decoupling contact, and spring metallurgy. Thus,it is advantageous to affix the lip structures 900 to the ends of thecontact wires 906. The guide plates 908 and 910 will then direct boththe contact wires 906 and the tip structures 900 with parallel orientedblades 902 of the present invention affixed thereto across the terminalsof an electronic component under test. In this manner, variousembodiments of the present invention may be used in conjunction withCobra style probes to provide a more reliable electrical connectionbetween the Cobra style probes 906 and the terminal of the electricalcomponent under test.

Alternatively, FIG. 9B illustrates another embodiment of the presentinvention having parallel oriented blades 912 at the ends of contactwires 906. In the same manner as described previously with respect toFIG. 2D, the blades 912 may be formed at the end of the contact wires906 by, for example, a plating or machining process. Thus, the contactwires 906 have a blade tip or “chiseled head” 912 without the use of atransferred tip structure. Note also, that each of the alternativeembodiments discussed above and below in reference to FIGS. 6A, 6B, 7A,7B, 7C, 8A, and 8B may be modified for use with a blade (such as blade912) formed at the end of an interconnection element that does not use atransferred tip structure.

Although the preferred embodiment of the present invention has thesharpened blade of the tip structure oriented such that the length ofthe blade is substantially parallel to the horizontal movement of thetip structure as the tip structure deflects across the surface of theterminal of the electronic component under test, an alternativeembodiment orients the blade such that the length of the blade ispositioned at a slight angle off parallel. For example, one embodimentmay encompass a blade oriented at an angle such that the length of theblade is within approximately 45° of the axis parallel to the horizontalmovement of the tip structure as the tip structure deflects across thesurface of the terminal of the electronic component under test. Ideally,the blade(s) will be at an approximate ±30° angle to the paralleloriented axis. Thus, this embodiment is able to provide a modifiedscraping motion across the surface of the terminal under test whileminimizing the amount of buildup accumulating along the blade 800.

Equipment for probing often includes an aligning feature. Such aligningequipment may comprise optical sensors using light beams to detect thereflection off the tip structures. Each of the above describedembodiments may be further improved to include a blade design having abetter reflection. More reflective blades and/or tip structures wouldprovide a method for automatic recognition for classification andalignment purposes (e.g., alignment operations performed automaticallyin a wafer prober). The reflective ability of a blade is dependent on aflat upper surface at the tip of the blade (i.e. a blade having across-section of a truncated pyramid). The amount of reflection iscontrolled by controlling the length of time the initial trench (i.e.the trench used to form the blade) is etched, such that the trench doesnot come to a sharp point at its tip. Another method of controlling theamount of reflection per blade involves inserting reflow glass in thebottom of the trench before depositing the aluminum and copper layers.The glass at the tip of the trench softens the edge (or tip) of theblade and results in a blade having a cross-section similar to atruncated pyramid. Alternatively, the blade tips could be made having asharpened edge in the manner described above with the sharpened edgethen sanded (or grinded) down such that the blade has a flat top edgethat is reflective. Both of these alternative methods of creating areflective blade are easy to incorporate into the manufacture process.

Thus, an apparatus and method providing improved interconnectionelements and tip structures for effecting pressure connections betweenterminals of electronic components is described. The sharpened bladeoriented on the upper surface of the tip structure such that the lengthof the blade is substantially parallel to the direction of horizontalmovement of the tip structure as the tip structure deflects across theterminal of an electronic component under test provides numerousadvantages over the prior art. The substantially parallel oriented bladeallows the tip structure of the present invention to slice cleanlythrough any non-conductive layers on the surface of the terminal andeffect a reliable electrical contact without damaging the surface of theterminal or acquiring particle buildup along the surface of the blade.Further, the parallel orientation of the blade of the present inventionmaximizes contact between the tip structure and the terminal such thatelectrical contact is not lost as the tip structure deflects across theterminal, even with terminals having smaller contact areas.

We claim:
 1. An electrical apparatus, comprising: at least one blade onan end of an interconnection element, said blade having a given lengthand oriented on the interconnection element such that said length runssubstantially parallel to a horizontal wiping motion of said bladerelative to an electrical terminal when the interconnection element isplaced in wiping contact with the electrical terminal.
 2. The electricalapparatus of claim 1 wherein the horizontal motion of said blade occurswhen said blade makes an electrical contact with the electricalterminal.
 3. The electrical apparatus of claim 2 wherein said blade hasa truncated pyramid cross-sectional structure.
 4. The electricalapparatus of claim 2 wherein said blade has a sharpened edge along saidlength of said blade.
 5. The electrical apparatus of claim 4 whereinsaid blade has a cross-sectional structure with a front edge at a firstend of said length of said blade and a back edge at a second end of saidlength of said blade.
 6. The electrical apparatus of claim 5 whereinsaid front and back edges are rectilinear.
 7. The electrical apparatusof claim 5 wherein said front and back edges are pyramidal.
 8. Theelectrical apparatus of claim 5 wherein said front and back edges havetwo sides such that said blade has a hexagonal shape.
 9. A tipstructure, comprising: a foot having an upper and a lower surface; and,at least one blade on said upper surface of said foot, said blade havinga given length and oriented on said foot such that said length runssubstantially parallel to a horizontal wiping motion of said foot. 10.The tip structure of claim 9 wherein the horizontal motion of said footoccurs when said tip structure makes an electrical contact with anelectrical terminal.
 11. The tip structure of claim 9 further comprisinga resilient contact element coupled to said lower surface of said foot.12. The tip structure of claim 9 wherein said blade has a sharpened edgealong said length of said blade.
 13. The tip structure of claim 12wherein said blade has a primary edge at a front end of said blade and atrailing edge at a back end of said blade.
 14. The tip structure ofclaim 12 having a first and a second blade on said upper surface of saidfoot.
 15. The tip structure of claim 14 wherein said first and secondblades are joined by a bridge.
 16. The tip structure of claim 14 whereinsaid first and second blades are in a juxtaposed position.
 17. The tipstructure of claim 12 wherein said blade has a triangularcross-sectional structure with a front edge at a first end of saidlength of said blade and a back edge at a second end of said length ofsaid blade.
 18. The tip structure of claim 17 wherein said front andback edges are rectilinear.
 19. The tip structure of claim 17 whereinsaid front and back edges are pyramidal.
 20. The tip structure of claim17 wherein said front and back edges have two sides such that said bladehas a hexagonal shape.
 21. A tip structure, comprising: a foot having anupper and a lower surface; and, at least one blade on said upper surfaceof said foot, said blade having a given length and oriented on said footsuch that said length is within approximately ±45° of an axis parallelto a horizontal wiping motion of said foot.
 22. The tip structure ofclaim 21 wherein said blade has a sharpened edge along said length ofsaid blade.
 23. The tip structure of claim 22 having a first and asecond blade on said upper surface of said foot.
 24. The tip structureof claim 23 wherein said first and second blades are joined by a bridge.25. The tip structure of claim 23 wherein said first and second bladesare in a juxtaposed position.
 26. The tip structure of claim 22 whereinsaid blade has a triangular cross-sectional structure with a front edgeat a first end of said length of said blade and a back edge at a secondend of said length of said blade.
 27. The tip structure of claim 26wherein said front and back edges are rectilinear.
 28. The tip structureof claim 26 wherein said front and back edges are pyramidal.
 29. The tipstructure of claim 26 wherein said front and back edges have two sidessuch that said blade has a hexagonal shape.
 30. An electrical contactstructure comprising: a plurality of interconnection elements disposedin relationship with one another; a plurality of tip structures affixedto respective ones of said interconnection elements, each of said tipstructures further comprising: at least one blade on a contact point ofa respective one of said interconnection elements, said blade having agiven length and oriented on the respective one of said interconnectionelements such that said length runs substantially parallel to ahorizontal wiping motion of the respective one of said interconnectionelements when the respective one of said interconnection elementsdeflects across a terminal of an electrical component to make anelectrical contact.
 31. The electrical contact structure of claim 30wherein the horizontal motion of said blade occurs when said tipstructure makes electrical contact with an electrical surface.
 32. Theelectrical contact structure of claim 31 wherein said blade has asharpened edge along said length of said blade.
 33. The electricalcontact structure of claim 32 wherein said blade has a triangularcross-sectional structure with a front edge at a first end of saidlength of said blade and a back edge at a second end of said length ofsaid blade.
 34. The electrical contact structure of claim 33 whereinsaid front and back edges are rectilinear.
 35. The electrical contactstructure of claim 33 wherein said front and back edges are pyramidal.36. The electrical contact structure of claim 33 wherein said front andback edges have two sides such that said blade has a hexagonal shape.37. A method of making an electrical contact structure, comprising thesteps of: forming a trench in a sacrificial substrate; depositing atleast one layer of at least one conductive material in said trench toform a blade having a given length, an upper surface, and a lowersurface; and, coupling an interconnection element to said lower surfaceof said blade, wherein said blade is oriented such that said length ofsaid blade runs substantially parallel to a horizontal wiping motion ofsaid blade.
 38. The method of claim 37 further comprising the step ofreleasing said blade from said sacrificial substrate.
 39. The method ofclaim 38 wherein said step of releasing said blade from said sacrificialsubstrate further comprises releasing said blade from said sacrificialsubstrate by a process selected from the group consisting of heat andchemical etching.
 40. The method of claim 37 wherein said step offorming a trench further comprises etching a trench in a substrate witha potassium hydroxide selective etch.
 41. The method of claim 40 whereinsaid step of etching a trench further comprises etching a trench in asubstrate with a potassium hydroxide etch between the 111 and 001crystal orientation.
 42. The method of claim 37 wherein said step offorming a trench further comprises forming a trench in a substrate,wherein said trench has a triangular cross-section.
 43. The method ofclaim 37 wherein said step of forming a trench further comprises forminga trench in a substrate, wherein said trench has a truncated pyramidcross-section.
 44. The method of claim 37 wherein said step of couplingsaid interconnection element to said lower surface of said blade furthercomprises soldering said interconnection element to said lower surfaceof said blade.
 45. The method of claim 37 wherein said step of couplingsaid interconnection element to said lower surface of said blade furthercomprises brazing said interconnection element to said lower surface ofsaid blade.